^ To be fair, the P5-Three is only supposed to give up ~10g of drag to the P5-Six from the different fork+brake cover.

In short, the P5 was designed to increase drag on the frame, but decrease overall drag on bike+rider.

Still, this test and Inside Triathlon's confirms that the quality of frames (from a performance perspective) is really quite high amongst most of the leaders, and not ton of speed is given up if you instead opt for the one you prefer, for handing, aesthetic, etc. reasons.

damon_rinard wrote:

Tour Magazin have really improved their wind tunnel testing. Robert Kuehnen and I talked a bit at Eurobike and via email, and I'm glad to see they've adopted many of our suggestions. And - to their credit - they declined to allow us (or any bike company) attend their tunnel test.

However, when comparing data, please remember the P5 has a drag increase on the frame, which is there to reduce drag on the rider's back - and Tour magazine's set up has no back. We haven't tested legs-only, so sorry, I don't have an estimate as to the magnitude.

Seat tube aero zone As part of our aero zone research, we’ve isolated areas where slightly unconventional airfoil shapes can work well, again taking into account the local airflow. Specifically, it’s rare that a truncated airfoil works well in typical flows, since the aft low pressure recirculation zone “sucks” on the back of the object, adding drag by “pulling” backward on the frame or component’s rear-facing surfaces.

Figure 13 Air flow characteristics over a semi-aerodynamic body. Stalled flow in aft wake indicates a low-pressure zone that adds drag by “sucking” on aft-facing surfaces. This drag can be reduced by completing the sharp trailing edge shape of the body, tapering the surfaces to follow the lines of the natural air flow.

However, in particular locations a well-designed truncated foil can help in both expected and in unexpected ways. For example, it generally works well to truncate an airfoil to allow the following components to draft. For example, Cervélo pioneered the seat tube cutout that allows the rear tire to draft in the truncated space behind the seat tube.

On the other hand, it’s counterintuitive that the P5’s truncated seat post and seat tube foils reduce drag, since truncated airfoils without a following body normally increase drag. In fact, the P5 uses the low pressure zone created by these truncated foils to redirect the air coming off the rider’s legs & back, delaying separation and reducing aerodynamic drag on the rider and bike system, despite slightly increasing drag on the bike itself.

Figure 14 CFD image showing air velocity contours. Low speed air behind the seat post and seat tube (blue) indicates a low pressure zone, which normally increases drag but in this case pulls the air down the rider’s back to delay separation (arrow), thus decreasing drag.

This is an unusual exception, and only proves the rule that it’s best to use truncation only where it makes sense. This breakthrough was possible because Cervélo has been testing and designing bikes with riders for many years now. One effect is that a P5 tested without a rider shows a slight increase in drag; the rider must be present to gain this aero benefit.

So all we need now is for Tour to attach a torso, arms & head (with typical helmet) to their moving legs, placed in a 'typical' position, while still excluding the manufacturers from being present at the test.

Huge problem is not even having arms. I mean, that high v setup on the P5 and the non flush stem have no drag penalty with a rider on board, but without, it's definitely a disadvantage compared to the Canyon and BMC (and other bikes)

I was impressed by the Canyon until I looked at the geometry - pointless to have a UCI legal frame with reach of 457. And short F-C with long chainstays is also not an example of brilliance. Which is a pity as they appear to have put a lot of thought into the aero aspects. If anyone has dimensional data for the bars that would be useful.

There are a couple of aspects in which this test counts against the P5. And the major curse of the P5 is not being able to easily get Aduro bars on a three - so the performance of mine will be well behind what is shown here.

So I think the winner from the test is the Slice RS - decent size range (not as expansive as the P5), UCI legal and has lower pricing for the base model.

With a dummy then you get into; which rider do you model, which position, how do you adjust fit of different bikes, do you test 2 fits on 2 sizes to see which is optimal, if the same rider has different optimal positions on 2 different bikes, do you use those, or do you keep the same position for all bikes, what if a particular bike tests better at yaw, but the position you use is not optimal at yaw....... etc etc etc

I was impressed by the Canyon until I looked at the geometry - pointless to have a UCI legal frame with reach of 457. And short F-C with long chainstays is also not an example of brilliance. Which is a pity as they appear to have put a lot of thought into the aero aspects. If anyone has dimensional data for the bars that would be useful.

I found somewhat of an explanation on a VeloNews from the 2012 Giro d'Italia when the bike was launched.

"Canyon went with considerably longer-than-average chainstays and wheelbase, and a long top tube (a medium has a 594mm top tube), and paired them with relatively short stem. The concept is similar to that used on modern trail and all-mountain bikes – making the frame longer and the stem shorter provides high-speed stability and improved handling. Cornering may be a touch slower, but a steep 73.5 head tube and adjustable-rake fork should balance the system out. More importantly, the bike should be highly stable at race speeds."

So I think the winner from the test is the Slice RS - decent size range (not as expansive as the P5), UCI legal and has lower pricing for the base model.

There is no bike that is more of a pain to work on than the SliceRS. Want to replace a rear derailleur cable? get ready to pop the cranks off. Remove the rear brake cover? don't squeeze the rear brake too hard, you'll break the internal bb cable guide. No good place for barrel adjusters=good luck trying to accommodate two wheelsets of different widths. I could go on, but...PS. I hate this bike.

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